This is a map of US military bases in the Persian Gulf area. They just happen to encircle Iran.
This is the Persian Gulf. Wikipedia says:
The Persian Gulf and its coastal areas are the world's largest single source of crude oil and related industries dominate the region. Safaniya Oil Field, the world's largest offshore oilfield, is located in the Persian Gulf. Large gas finds have also been made with Qatar and Iran sharing a giant field across the territorial median line (North Field in the Qatari sector; South Pars Field in the Iranian sector). Using this gas, Qatar has built up a substantial liquified natural gas (LNG) and petrochemical industry.
In 2002, the Persian Gulf nations of Bahrain, Iran, Iraq, Kuwait, Qatar, Saudi Arabia, and the UAE, produced about 25% of the world's oil, held nearly two-thirds of the world's crude oil reserves, and about 35% of the world natural gas reserves. The oil-rich countries (excluding Iraq) that have a coastline on the Persian Gulf are referred to as the Persian Gulf States. Iraq's egress to the gulf is narrow and easily blockaded consisting of the marshy river delta of the Shatt al-Arab, which carries the waters of the Uphrates and the Tigris rivers, where the east bank is held by Iran.
The New York Times informs us that Iran could hit us in the pocketbook if they decided to block access to and from the Persian Gulf.
HOUSTON — If Iran were to follow through with its threat to blockade the Strait of Hormuz, a vital transit route for almost one-fifth of the oil traded globally, the impact would be immediate: Energy analysts say the price of oil would start to soar and could rise 50 percent or more within days.
An Iranian blockade by means of mining, airstrikes or sabotage is logistically well within Tehran’s military capabilities. But despite rising tensions with the West, including a tentative ban on European imports of Iranian oil announced Wednesday, Iran is unlikely to take such hostile action, according to most Middle East political experts.
United States officials say the Navy’s Fifth Fleet, based in nearby Bahrain, stands ready to defend the shipping route and, if necessary, retaliate militarily against Iran.
Iran’s own shaky economy relies on exporting at least two million barrels of oil a day through the strait, which is the only sea route from the Persian Gulf and “the world’s most important oil choke point,” according to Energy Department analysts.
Our wealth depends on our military power. Our military power and the corporations that profit from it depend on a reliable supply of affordable oil.
We are the world's largest superpower and we take what we want. When we act, we will be told that we are defending ourselves from terrorists. If this happens under a conservative president, the left will object. If this happens under a liberal president, 35% of the left will protest and everyone else will not.